The FBI said Friday that it investigated and spoke with Tsarnaev — who died late Thursday night in a shootout with Boston police — in 2011, at the request of a foreign government. But it “did not find any terrorism activity, domestic or foreign.” His brother, Dzhokar Tsarnaev, was captured by police late Friday night in Watertown, Mass.

“The ball was dropped in one of two ways,” Graham said on CNN’s “State of the Union.”

“The FBI missed a lot of things is one potential answer — or our laws do not allow the FBI to follow up in a sound, solid way.”

Sen. Chuck Schumer (D-N.Y.) pointed out the “red flags” that Tsarnaev threw up and said that there are still a lot of questions the FBI has to answer about its 2011 investigation.

“There was a lot to be learned from this guy. He was on websites talking about killing Americans. He went overseas, as Chuck had indicated. He was clearly talking about radical ideas. He was visiting radical areas. And the fact that we could not track him has to be fixed. It’s people like this that you don’t want to let out of your sights. … This was a mistake.”

“Anytime we question him about his guilt or innocence, he’s entitled to his Miranda Rights and a lawyer, but we have the right under our law …to gather intelligence from enemy combatants, and a citizen can be an enemy combatant,” Graham said.